A mysterious figure needs adventurers to track an ancient artifact and an even more ancient ritual that might not even exist. The adventure will take them to jungles of Chult, ruins of Netheril Empire and more.
For ages, two Guardian Nagas called Kashtasha and Ssaptishi protected an ancient artifact in ruins long forgotten. They spent their days researching spells to better protect the artifact and discuss philosophy or other scholarly topics.
Although they got along well, they never saw eye to eye on two topics. First, while Kashtasha had the regular defensive, non-violent nature of a guardian naga, Ssaptishi thought that offense was the best defense. If someone made it to their lair, it stood to reason that they would be after the artifact and as such, they needed to be dealt with, which Kashtasha found too aggressive, worryingly so at some times)
Second was the topic of Spirit naga. Kashtasha believed they were creatures inherently born evil while Ssaptishi thought they could be Guardian nagas who transformed into spirit nagas and there might be more to them than meets the eyes.
One day, adventurers found their lair by chance. They were kind adventurers that were clearly beneath the Nagas’ power. Ssaptishi wanted to attack, not necessarily to kill, but to intimidate and make sure they never come back. Kashtasha stopped Ssaptishi, saying there was no reason to be worried about these upstarts and talked with them. After a nice conversation, the party left. Kashtasha shamed Ssaptishi for even thinking to attack those nice people.
Later in the week, they went in the depths of their lair to rest and realized the artifact was gone. Confused, Kashtasha cast some scrying spells and learned the truth: The party had one more member, who went in to steal the artifact while they were distracted talking to them.
Kastasha was devastated but Ssaptishi was mad. Ssaptishi hated the adventurers for stealing the artifact, the nagas’ lives’ purpose for centuries, hated Kastasha for sympathizing with those wreteched adventurers and hated himself for allowing all this to happen. He left on a path for vengeance.
In shock, watching his centuries-long friend leave, Kastasha noticed that Ssaptishi was probably right about Spirit nagas: Ssaptishi’s color had started changing and Kastasha knew he would never go back to his old self. Whatever good and peace left in him was gone.
After Ssaptishi’s departure, Kastasha goes through his research about Spirit Naga and better understands his old friend’s transformation. She suspects there is a ritual that might reverse it — at the cost of her own life. As she sees herself responsible for what happened, she thinks that’s fair and she’s willing to sacrifice herself to bring his friend back to light.
For that, she needs two things: To investigate if a such ritual exists in the first place and what’s needed for it, and track the artifact as she knows Kastasha will do the same.
Tracking the ritual will require doing research in places like Candlekeep, exploring ruins with old tomes and encounters with wizards and hoarders of the arcane, possibly a lich or a dragon — be they friend or foe. Eventually, it will take them to Chult, as the Bone Naga ritual created by Naga’s rivals, the Yuan-ti, will prove to be the key.
For the artifact, they’ll investigate the party that stole the artifact in the closest city, checking inns, magic item merchants and others and find out that they were in the business of collecting old, forgotten items and finding ways to extract them with minimal risk. Their next targets are in some Netherese ruins, so the road will take the naga there.
As it’s challenging to do all of this alone, especially the first steps that need to be done in the city, so she finds adventurers to work with her.
The above already provides a bunch of points, but this is very pluggable. The thief party might be anywhere, the magic ritual could also require knowledge from any part of the world. The thief party could actually be good aligned, need the artifact(s) for a good cause. Maybe they aren’t collectors at all. There could even be a big plot twist — maybe they are an evil party targeting naga, trying to turn them to evil, recruited by a priest whose god wants to recruit them.